This invention is directed to a device, viz., a membrane or diaphragm-free electrolytic cell device, for use in treating waste waters, particularly those resulting from metal plating operations and known as platers' rinse waters, to remove metal pollutants (and optionally also cyanide) therefrom prior to discharge of the treated effluent into streams, rivers, etc.
There is considerable and growing concern over pollution of the nations' waterways with various contaminants such as heavy metals, e.g., copper, nickel, zinc, mercury, cadmium, etc., and such nonmetallic contaminants as cyanide as well as complexes of the foregoing metals with cyanide, etc.
Many of these pollutants enter the nations' waters from industrial sources, such as metal finishing or plating plants and from mining sources. Environmental legislation and regulations, on the federal, state and local government levels, have set forth maximum allowable concentrations of these contaminants which may be discharged into public waters.
A clear and present need exists for an economical yet effective device for treating such waste waters to permit removal of a substantial portion of contaminants, especially with respect to platers' rinse water, which customarily contains one or more of such metals as copper, zinc, cadmium, alone or in combination with cyanide.
Various methods have been proposed or are reported to be available for use in removal of metals and/or cyanide from water.
One device for removing heavy metals from waste water is the apparatus set forth by Howard L. Recht in U.S. Pat. No. 3,954,594 which comprises an electrochemical cell provided with separate anode and cathode compartments, each containing a bed of electrically conductive particles. The compartments are separated by an electrically nonconductive foraminous member, e.g., a water-impermeable plastic, e.g., nylon, cellophane, or ceramic material, such as oxides of silicone, zirconium, tantalum, beryllium and mixtures thereof. Suitable electrically conductive particles for use in the anode compartment include graphite, tantalum, stainless steels, and the metals of Group VIII of the Periodic Table of the Elements. Suitable materials for the particles for use in the cathode compartment include copper, nickel, tin, zinc, silver and gold. The apparatus is disclosed in the patent as capable of removing heavy metal and cyanide pollutants from aqueous streams containing them.
U.S. Pat. No. 4,197,181 to C. Portal et al. is directed to a stationary particle bed dual electrode for electrowinning of metal values from solutions containing them. Each particulate bed electrode assembly comprises an electrically nonconductive support frame holding a perforated, electrically conductive flat distributor plate through which the solution to be treated flows. Attached to the side of the perforated distributor plated facing the internal cavity defining the stationary particulate bed is a coarse filter strainer. Each stationary particulate bed can be comprised of conductive, carbonaceous particles onto which the desired metal values deposit. An interface liner, e.g., synthetic filter cloth, is utilized on one side of the conductive, perforated distributor plate, and a polyurethane foam filter element is employed on the opposite side thereof. The interface liner is employed to discourage bonding of the particulate bed particles to the liner through the action of dendrites growing through the liner. The polyurethane filter element is utilized for flow distribution and elimination of any particulate material in the electrolyte solution before passing through the perforated plate.
U.S. Pat. No. 4,226,685 also issued to C. Portal et al. (represented to be a continuation-in-part application of U.S. Pat. No. 4,197,181) is directed to a method of treating plating wastes containing at least one heavy metal and (optionally) cyanide ions such that ionic contaminants are reduced to acceptably low concentrations, and the plated metals are available in a concentrated and thus retrievable form. This Portal et al patent appears to utilize the same apparatus as set forth in U.S. Pat. No. 4,197,181, viz., a stationary dual particulate bed apparatus utilizing dual electrodes with a central cavity and including filters for trapping particulate matters suspended in the plating wastes. In the sole example of U.S. Pat. No. 4,226,685, the inlet stream contained 150 parts per million of copper as cupric sulfate and 20 gallons of such solution was processed in 6 hours in 2 passes through the apparatus, each pass lasting 3 hours. The outcome of copper concentration as a result of the first pass was 33 parts per million and the outcome copper concentraiton as a result of the second pass was 15 parts per million.
U.S. Pat. No. 3,694,325 to S. Katz et al. is directed to a process for producing a 3-dimensional, reticulated electroform by first electrolessly then electrolytically depositing metal on a flexible tester-type polyurethane foam followed by heating the metallized foam to about 800.degree. F. in an oxidizing environment, i.e., air, to decompose the polyurethane substrate, viz., pyrolyze it from the electroform. Then a second heat treatment, at higher temperatures, can be employed in a reducing atmosphere to anneal the pyrolyzed electroform. Although there is a statement at column, lines 1 to 2, that the substrate may or may not be removed after plating; the remaining portion of the specification, including all the specific detailed disclosure and the sole example requires the aforementioned pyrolysis of the polyurethane foam substrate.
An article entitled "IMPROVEMENT OF THE HIGH-RATE DISCHARGE BEHAVIOR OF THE NICKEL ELECTRODE" by Guy Crespy et al. appearing at pages 219 to 237 of the published Proceedings of the 11th International Symposium held at Brighton, September, 1978, and published at POWER SOURCES 7 (RESEARCH AND DEVELOPMENT IN NON-MECHANICAL ELECTRICAL POWER SOURCES) copyright 1979 by Academic Press, is directed to the utilization of a nickel foam-type electrode structure in alkaline batteries. The nickel foam-like structure is obtained by impregnating ether-type organic polymer foams, such as polyurethane foams, having most of their pores intercommunicating, with a nickel powder followed by heating the nickel powder-impregnated polyurethane foam at temperatures sufficiently high to effect the pyrolization of the polyurethane substrate. The pyrolysis is conducted by placing the nickle powder-impregnated foam in an oven under a very light pressure (approximately 2 grams cm.sup.-2) while slowly raising the temperature under a reducing atmosphere until the organic material decomposes into volatile substances (up to 450.degree. C.) and is quantitatively eliminated. The resulting powder is then sintered at temperatures of about 700.degree. to 1000.degree. C. Typical sintering conditions employed were 1000.degree. C. for one hour. The resulting electrode substrates were then impregnated in a one-step cathodic precipitation of nickel hydroxides to impregnate the electrode with active material. The Crespy et al. nickel foam electrodes impregnated with nickel hydroxides are utilized in the so-called dry cell or storage batteries of the alkaline type.
An article "CHARACTERIZATION OF RETICULATE, THREE-DIMENSIONAL ELECTRODES" appearing in the JOURNAL OF APPLIED ELECTROCHEMISTRY 8 (1978) at pages 195 to 205 by A. Tentorio et al. is directed to the preparation of a reticulate electrode by first electrolessly then electrolytically depositing copper on a polyurethane foam substrate. This reticulate electrode is then assemblied in an electrolytic cell, as depicted in FIGS. 2 and 3 of said Tentorio et al. article at pages 199 and 200, respectively. Each such electrolytic cell is comprised of a reticulate cathode of the metallized polyurethane foam as set forth above and a counter electrode, e.g., made of copper (FIG. 1) or lead/lead dioxide (FIG. 3) with an ion exchange membrane. The purpose of the ion exchange membrane is to separate the anolyte and catholyte feeds. At page 205 of the Tentorio et al. article, the authors observe that the cell of FIG. 3 could operate in waste water treatment only with multiple-pass electrolysis and that the level of concentration of pollutant after treatment should not be below tens of parts per million in order not to weigh down excessively the recycle.
The electrolytic waste water treatment device of this invention enables the removal of metal from platers' rinse water with or without recycling. It offers a more direct treatment procedure in that the present device does not require the use of an ion exchange membrane to separate the anolyte and catholyte. Additionally, the present cell provides a system whereby the solution to be treated flows through one compartment in each cell. The cell system is flexibly designed to accommodate any type of anode, e.g., graphite, DSA, lead, aluminum, etc., and reticulate cathode.
The device is of simple construction and therefore inexpensive. The cell provides ready access to the cathodes so that they can be quickly and easily removed. The device allows for introduction of fresh cathodes at the rear of the electrode pack while moving forward those electrodes which previously were in the rear of the pack so that they may be fully plated. This allows for more efficient use of the cathodes, thus reducing the cost of operation. Additionally, the metal plated cathode structures can be recovered and sold for scrap. This scrap metal from the loaded cathode structure is routinely in a +99 percent pure form for treatments in which only one metal contaminant exist in the effluent stream. The metal contaminants, copper, cadmium, nickel, zinc, silver, gold, can be removed routinely from the inlet solution of approximately 150 ppms producing an outlet solution of approximately 15 ppms in the single pass mode in which a cell of 50 copper reticulate cathodes and 51 anodes of the graphite or DSA type are employed. In a recycling system, cyanide can be oxidized to cyanate while concurrent metal removal is occurring at the copper reticulate cathode. The cyanide can be oxidized routinely from the inlet solution of approximately 150 ppms producing an outlet solution of approximately 10 ppms cyanide and approximately 220 ppms cyanate. This concurrent system is utilized at highly alkaline pH, viz., at pH values ranging from above about 11, e.g., from about 11.sup.+ to about 13.